Marcel Lehr

Comparison of axial flux and radial flux machines for the use in wheel hub drives

This report compares axial flux and radial flux machines for the use in wheel hub drives in terms of their electromagnetic and thermal properties. First, the differences between the topologies of the two types of machines are explained, and a theoretical comparison of the possible power densities is carried out. Then, the machines are designed, using a finite-element software with special consideration on the number of slots per pole and phase. Finally, the designs are thermally and electromagnetically compared.ZusammenfassungDer vorliegende Beitrag vergleicht Axial- und Radialfluss-Maschinen für den Einsatz in Radnabenantrieben hinsichtlich ihrer elektromagnetischen und thermischen Eigenschaften. Zunächst werden dabei die topologischen Unterschiede der beiden Maschinentypen erläutert und ein theoretischer Vergleich der möglichen Leistungsdichten durchgeführt. Anschließend werden die Maschinen unter besonderer Berücksichtigung der Lochzahl mit Hilfe der Finite-Elemente-Methode ausgelegt. Abschließend werden die Auslegungen thermisch und elektromagnetisch miteinander vergleichen.

Design and construction of a permanent magnet excited Flux-Switching-Machine

In this paper the design and the construction of a permanent magnet excited Flux-Switching-Machine (FSPM) are summarized. The FSPM-Machine is a permanent magnet synchronous machine, which is characterized by the attachment of the permanent magnets in the stator of the machine.

Design, construction and measurements of a permanent magnet axial flux machine

The results of the design, the construction and first measurements of an axial flux permanent magnet (AFPM) machine are summarized. The goal of this project was to build an axial flux machine with surface mounted magnets in the simplest possible way to use the machine as a demonstrator for small wheel hub drives with a reduced torque demand. Therefore the machine was designed as double-sided motor with internal stator and tooth-coil winding to enable a modular structure and two rotor discs. For the ease of a simple integration of the machine, the outer diameter was limited to a certain value. Therefore the design yield to a machine with 12 poles and 18 stator teeth (number of slots per pole and phase q = ½). 3D-electromagnetic and 3D-thermal studies with the finite-element-method (FEM) software JMAG were carried out. After the design of the active elements, the construction of the prototype was done. The machine was build up on a test bench and coupled with a load machine to compare the simulation results with the measurements. The measurements show that the electromagnetic properties (torque, efficiency) fit with the simulation results, but due to the open ventilation motor design the thermal behavior of the machine is better than assumed for the simulations. With the results it is possible to estimate also the behavior of bigger wheel hub drives.

Determination of efficiency of permanent magnet synchronous machines from summation of losses

The determination of the efficiency of electrical machines by direct measurements is often too imprecise if the efficiency exceeds 95 %. For electrically excited synchronous machines a standardized method exists to determine the efficiency by summation of the individual losses. This method needs a variable excitation and therefore cannot be used for permanent magnet synchronous machines. As permanent magnet machines are increasingly used as wind turbine generators and traction motors, there is a large demand for an alternative method. In this project a new procedure is developed, which consists of a calculation of the losses at rated conditions via three different measurement series. The corresponding losses and circuit diagram parameters are determined from measurements at open circuit, measurements with removed rotor and measurements with pure reactive current. In addition to the theoretical calculations direct efficiency measurements are used to validate the efficiency calculation results. The two examined permanent magnet motors with fractional slot winding have a rated power of 45 kW.